A dialyzer connecting coupler which connects a solution transferring line such as a dialysis solution circulating hose to a connection coupler of a dialyzer is shown in FIG. 3 by way of example. In this dialyzer, a fitting portion 32 into which a connection plug is to be removably fitted and a cavity portion 33 for communicating with the inside of the connection plug are formed in the inside of a body 31, and a tube-shaped, hose connecting portion 34 is formed integrally with the body 31 in a laterally projecting shape, and its inside communicates with the cavity portion 33. In addition, an O-ring 35 for liquid-tightly connecting the connection plug and the fitting portion 32 is provided in the body 31, and the body 31 is provided with a fixing mechanism 36 which releasably fixes the connection plug to the body 31.
In recent years, in view of greater improvements in substance permeation performance of dialyzers due to higher performance thereof, more attention has been drawn to the risk that a pyrogenic substance such as an endotoxin will enter into blood from a dialysis solution. From this possibility, the necessity to purify dialysis solutions has increased, and various contrivances have been made. For example, during actual production of a dialysis solution, RO water (water processed by a reverse osmosis film) is used, and during dialysis, an endotoxin removing filter is disposed in front of the dialyzer.